Measuring Diversity

First, we need a way to measure racial diversity. The most commonly used measurement is the Gini-Simpson Index, hereafter referred to as “the Diversity Index” in title-case.

The value of this index for a given municipality can be interpreted as the probability that two randomly selected residents are of a different race. For example: Two random residents in Jersey City have a 75% chance of identifying as different races.

Disha Raychaudhuri of NJ Advance Media calculated the Diversity Index for every town in NJ, but only made the results for the 25 most diverse towns available. I was able to reproduce their results² and provide them in full below. While Raychaudhuri restricted their analysis to towns with more than 10,000 residents, I include towns with more than the median population: 8,244.³

The Cornwall Center for Metropolitan Studies made a map of the Diversity Index for every Census tract, or “neighborhood”, in New Jersey, using data from 2009 to 2013. There’s also the national Racial Dot Map produced by the Weldon Cooper Center for Public Service.

The Data

I got data on the racial makeup of every municipality in the state from the American Community Survey (ACS), conducted by the US Census every year.⁴ This gives me a representative sample of everyone living in every town from 2013 to 2017, though the data are less reliable for places with lower population.

There are 7 racial groups in the ACS: White, Black or African American, American Indian and Alaska Native, Asian, Native Hawaiian and Other Pacific Islander, Two or more races, and Some other race. Because “Hispanic” is not a racial group (according to the Census Bureau’s admittedly imperfect definitions), I do not use the Hispanic grouping to calculate the Diversity Index. In doing so, I’m not leaving out Hispanic people. If you glance at the “HISPANIC OR LATINO ORIGIN BY RACE” summary table, you’ll notice most people identifying as “some other race” are Hispanic/Latinx in origin. All other Hispanic/Latinx people identify as White, Black, Asian, etc, and so they’re included in the count of the race with which they identify.⁵

The Results

The table below contains Diversity Index estimates and other indicators for every municipality in New Jersey with population counts greater than the median.⁶ To summarize, for most towns, the probability that two residents are a different race is less than 50%. In the median town, that probability is about 36.4%.

The vast majority of non-diverse towns are majority white. The chart below (with the red line marking 50% and the blue line marking the median) shows four towns with a Diversity Index below 50% and a racial group other than White in the majority: East Orange, Irvington, Willingboro, and Orange. In fact, there are very few places in NJ where less than half of residents are white.

Finally, the charts below show the racial makeup of the 30 most diverse and 30 least diverse places.

Notes